The 6-pack refers to the rectus abdominus muscle in the center of the human torso. While it looks like 6 different muscles, it's actually only 1 large muscle.
Then there is the transverse abdominals, which are more horizontal than the 6-pack muscles, and are also deeper in the abdomen itself.
Then on each side of your body are the internal and external obliques.
If you want strong and good-looking abs, work all of them and not just the 6-pack
